Modular Time Synchronized Injection Modules

ABSTRACT

In prior art grid systems, power-line control is done by substation based large systems that use high-voltage (HV) circuits to get injectable impedance waveforms that can create oscillations on the HV power lines. Intelligent impedance injection modules (IIMs) are currently being proposed for interactive power line control and line balancing. These IIMs distributed over the high-voltage lines or installed on mobile platforms and connected to the HV power lines locally generate and inject waveforms in an intelligent fashion to provide interactive response capability to commands from utility for power line control. These IIMs typically comprise a plurality of impedance-injection units (IIUs) that are transformer-less flexible alternating current transmission systems interconnected in a series-parallel connection and output pulses that are additive and time synchronized to generate appropriate waveforms that when injected onto HV transmission lines are able to accomplish the desired response and an provide interactive power flow control.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/721,749 filed on Aug. 23, 2018, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to reducing the harmonic component of impedance injection for balancing and control of power flow on the grid by providing a pseudo-sinusoidal voltage, built up by synchronous injection from a plurality of distributed injection modules that is smoothed to a sine wave by the impedance of the high-voltage power line.

BACKGROUND

Most power utilities use an energy management system (EMS)/supervisory control and data acquisition (SCADA) control systems for control of the power grid systems. FIG. 2 shows such a power generation-distribution system 200 with the substation-based static synchronous series compensators (SSSCs) 204 connected to power lines 108 and controlled directly by utility 206 over communication lines 207 for line balancing. In these cases, both power generators 203 and loads 205 are also shown connected at the substations. These control systems provide connection and communication between the power flow control units at the substations 204 from where distribution loads 205 are also connected. These utility-controlled systems are used to limit load imbalances over the power lines of the power transmission on the grid. As the systems are controlled by the utility 206 directly, they are slow to react to disturbances and imbalances on the grid. The systems as indicated are typically substation-based high power systems that are programmed to inject high voltages on to the high-voltage (HV) transmission lines 108.

These line balancing systems generate and inject impedance as high power square waves, which will cause harmonic oscillations in the power grid since the voltages that are required to be generated and injected for line control by these ground-based units are high. Hence these systems are typically designed to generate pseudo-sine waves as shown in FIG. 2A by using high voltage switches that switch at high-speeds and high power to generate a series of square waves of varying amplitudes, that when smoothed, provide the sinusoidal wave for injection on to the HV transmission lines 108. The use of the specialized power-hungry high voltage and high-speed switches, which require high reliability, transient blocking capability, high voltage insulation, and liquid cooling to remove the heat generated while switching, makes these substation-based units expensive to operate and maintain.

The current move in the industry is to use distributed and localized control in addition to utility based control of power flow over the HV transmission lines 108 using intelligent impedance injection modules (IIMs) that are coupled to the power line. FIG. 1 shows such an implementation. In FIG. 1, HV transmission lines 108 connected between generation points 104 and loads 106 are suspended from high voltage towers 110. The figure shows the IIMs 102 suspended on the power lines operating at the HV of the power lines. These IIMs with built-in intelligence are able to identify any local power flow control needs and any disturbance on the HV transmission line 108 and provide immediate and effective local corrective action by generating and injecting corrective impedance on to the HV transmission line.

A more advanced example of system 200 is shown in FIG. 3, as system 200A that includes distributed impedance injection modules (IIMs) 300 distributed over HV transmission lines 108 between substations 204. The IIMs 300 are directly attached to the HV transmission lines 108 of the power grid that are suspended insulated from ground on HV towers 201. Generators 203 and loads 205 are typically connected to the HV transmission lines 108 of the power grid at the substations 204. The IIMs 300 are communicatively connected or coupled to local intelligence centers (LINCs) 302 via high-speed communication links 303 that allow for communication and reaction by the IIMs 300 in the local area at sub synchronous speeds when required. The LINCs 302 are also connected by high-speed communication links 303 to other LINCs for coordination of activity of the local IIMs 300 groups. A supervisory utility 206A oversees the activity of the system 200A using command and communication links 207 connecting to the LINCs 302 and substations 204. The supervisory utility 206A is able to have interactive control of the local IIMs 300 via the communication links connecting it to the LINCs 302. FIG. 4 is a block diagram showing the main components of an intelligent IIM 300. Referring to FIG. 4, IIM 300 includes at least an impedance generation and injection module 100, an intelligent control capability 402 with at least a clock with time synchronization capability, and a high-speed communication link 410.

FIG. 5 shows an exemplary transformer coupled IIM 500 having two coupling transformers 506A and 506B that couple the IIM to the HV transmission line 108 to inject impedance on to the HV transmission line 108 to do line balancing and disturbance elimination. A secondary transformer 501 is used as a sensor unit for any disturbances on the power line and also to extract power from the power line to provide the necessary power for converters 505A and 505B to generate the impedances required to be injected on to the HV transmission line 108. The generation and injection are controlled by the input from the sensor and power supply unit 502 to a master controller 503 which provides input to controllers 504A and 504B coupled to the respective converters 505A and 505B.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements.

FIG. 1 is a block diagram illustrating conventional distributed impedance injection modules (IIMs) attached directly to an HV transmission line.

FIG. 2 is a diagram illustrating a conventional non-distributed control system based in substations with static synchronous series compensators (SSSC) for grid control.

FIG. 2A shows the generation of a pseudo-sinusoidal waveform generation using high-power high-frequency switches.

FIG. 3 is a diagram illustrating a conventional power grid system with a distributed and hierarchical intelligent control system.

FIG. 4 is a block diagram illustrating a conventional dynamic intelligent impedance injection module with local and global time synchronization capability.

FIG. 5 is a circuit diagram illustrating a conventional dynamic response capable IIM with transformer coupling to an HV transmission line of a grid.

FIG. 6 is a circuit diagram illustrating an example of a transformer-less flexible alternating current (AC) transmission system (TL-FACTS) based impedance injection unit (IIU), where one or more IIUs may constitute an impedance injection module IIM.

FIG. 6A is a circuit diagram illustrating a local master control module of a TL-FACTS-based IIU having an associated local clock according to one embodiment.

FIG. 6B is a circuit diagram illustrating a local master control module of a TL-FACTS-based IIU having an associated local clock that can be synchronized to a global clock according to one embodiment.

FIG. 7 is a block diagram illustrating an IIM having a series-parallel connection comprising four TL-FACTS-based IIUs according to one embodiment.

FIG. 7A is another exemplary block diagram of an IIM as a power flow control subsystem having nine TL-FACTS-based IIUs interconnected in a 3×3 Matrix, as an example, for use in a mobile power flow control application according to another embodiment.

FIG. 7B is an exemplary illustrative diagram of a mobile platform having three power flow control subsystems for the three high-voltage lines of a power grid.

FIG. 7C is an exemplary illustrative diagram of the subsystems as deployed by the mobile platform and connected to the power grid.

FIG. 8 is a block diagram illustrating the time delay between an exemplary group of IIMs distributed on an HV transmission line.

FIG. 9 is a diagram illustrating an exemplary smoothed sinusoidal waveform from a plurality of low impedance/voltage rectangular injected waveforms generated by a plurality of IIUs.

FIG. 10 is a diagram illustrating exemplary time-synchronized injection of rectangular waveforms injected on to an HV transmission line to achieve a pseudo-sinusoidal waveform.

FIG. 11 is a diagram illustrating the timing required for generation of the pseudo-sinusoidal waveform.

FIG. 12 is a diagram illustrating a local master control module with the processing capability for identification of disturbances on an HV transmission line according to one embodiment.

FIG. 13 is a flow diagram of a process for power grid system control using synchronized injection of impedance according to one embodiment.

FIG. 14 is a table showing time delays required to be synchronized to achieve a pseudo-sinusoidal waveform according to one embodiment.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosures will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosures.

Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the disclosure. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment.

Recently, transformer-less flexible alternating current (AC) transmission systems (TL-FACTS) that are lower in weight and cost have also been developed and implemented as IIUs for line balancing and control. An exemplary TL-FACTS-based IIU 600 is shown in FIG. 6. The TL-FACTS-based IIU 600 is powered by power extracted from the HV transmission line 108 via the secondary transformer 501 connected to the sensor and power supply block 502 and provided to the DC power source 604. Having DC power source 604 across the capacitor helps to improve the generation of the injected impedance across terminals 601A-B and optimize the impedance injection on to the HV transmission line 108. A local master control 503 is enabled with intelligence to respond to the power line disturbances and imbalances sensed by the sensor and power supply module 502 coupled to the power line 108. The master local control 503 also has a local clock therein which is synchronizable with external clocks. The master local control 503 has high-speed wireless linkage or interface 410 connecting to the neighboring IIMs and the LINCs 302 via the high-speed links 303 (as previously described). These high-speed communication links are used to provide the switching control and synchronization signals to the master local control 503 which in turn provide the necessary control instructions to the switch control blocks 603A-D of FACTS switches 602 where each FACTS switch 602 includes a control block (e.g., control blocks 603A-D) and FACTS device 605. FACTS device 605 includes a switching device (e.g., bipolar junction transistor (BJT), field-effect transistor (FET), metal-oxide-semiconductor field-effect transistor (MOSFET), or the like). Based on the switching control signals from master local control 503, each of the switch control blocks 603A-D controls its respective FACTS device 605, which in turn controls impedance injection terminals 601A-B that are connected in series across the HV transmission line 108. The TL-FACTS-based IIU 600, due to its low weight, allows a number of them to be connected or coupled to the HV transmission lines 108 and operate in series or parallel mode, or a combination thereof. A single or a plurality of inter-connected TL-FACTS-based IIU 600 may form a single IIM 300 that is connected directly to the high voltage power lines 108 and operate with a pseudo-ground at the HV powerline voltage. A protection switch 606 (i.e., open/close) is provided that is used to close and short the impedance injection terminals 601A-B during fault conditions on the HV transmission line 108 and hence to bypass the circuits of the TL-FACTS-based IIU 600 included in the distributed IIM 300 and protect the FACTS devices and control circuit from damage and failure.

As described, IIMs 300 extract power from the HV transmission line to generate and inject impedance on to the power lines in an intelligent manner to control and balance the power flow on the grid. The self-aware IIMs 300 having built in data processing capability and intelligence for local decision making are also provided with high-speed communication capability or interface 410 that allow sub-cyclic communication between the local IIMs 300 within a local area and the connected LINCs 302. The LINCs 302 distributed across the local areas are also enabled with highspeed communication capability that allow them to communicate at sub-cyclic speeds to neighboring LINCs 302. Hence, the distributed IIMs 300 are able to identify and react very fast to the changes and disturbances in the power line characteristics at the local level in a coordinated fashion. In addition, as detailed earlier, these intelligent IIMs 300 provide a capability to have localized control of line current and line balancing with interactive response capability where needed. Where necessary the IIMs 300 in neighboring local areas are able to work in coordination through the communicably coupled LINCs 302 to react to disturbances on the HV transmission line 108 and to provide response to instructions and commands from supervisory utility 206 and for local line management. The high-speed communication capability and hierarchical control capability are disclosed in the co-pending U.S. patent application Ser. No. 15/068,397, filed on Mar. 11, 2016, currently issued as U.S. Pat. No. 10,097,037, the disclosure of which is incorporated herein by reference in its entirety.

The IIMs 300 with or without transformers still inject square waves onto the power line, but at reduced amplitudes. Being of low amplitude injection, these individual impedance injections, typically in the form of voltages, tend to be less prone to generate harmonic oscillations on the HV transmission lines 108. But when high voltages are to be generated and injected on to the HV transmission line 108, for interactive control based on inputs from supervisory utility 206 for power system management and/or for power flow control and line balancing applications, one embodiment of the disclosed method uses a number of IIUs 600 of more than one distributed IIMs 300, from one or more local areas, that work together to inject impedance on to the power line. The injected voltages are then additive (or aggregated) and hence can create harmonic oscillations in the HV transmission line 108. Hence it is ideal if the impedance injections from this plurality of distributed IIMs 300 can be made pseudo-sinusoidal in nature, which can then be smoothed to a sinusoidal waveform without incurring the expenses of high-speed, high voltage switching circuits used prior substation-based implementations of static synchronous series compensators (SSSCs) 204 connected to power lines 108 and controlled directly by utility 206.

Another embodiment, as shown in FIGS. 7B and 7C, is to have a plurality of interconnected IIUs 600 forming IIM 300 assembled on one or more mobile platforms that can be transported and deployed as needed at locations along the HV transmission lines of any power grid system to provide any necessary interactive control capability.

Yet another embodiment is the ability to have plurality of interconnected IIUs 600 forming IIM 300 assembled at sub-stations as mobile units or ground based units and connected to the high-voltage power lines of the grid to provide any necessary interactive control capability.

According to one embodiment, a system for injecting impedance on to a high voltage (HV) transmission line is disclosed. The system includes one or more distributed impedance injection modules (IIMs) 300 coupled to the HV transmission line 108. Sensors attached to each power line, in some embodiments as part of each IIM 300 that includes a secondary winding or other alternate sensing capability, are configured to detect disturbance, power flow imbalance or other changes in the characteristics, such as temperature increases or vibration, of the HV transmission line 108 to which the sensors are attached. The sensed changes such as disturbance, flow imbalance or other change in the characteristics of the HV transmission line are communicated to the IIM 300, the LINCs 302 and the supervisory utility 206 over available communication links. A master control module 503 of the IIM 300 is configured to identify available resources on the HV transmission line, and generate and provide switching control signals to the identified resources for controlling impedance injection to provide interactive control capability to commands and instructions from the system supervisory utility 206 and also respond to any detected disturbance, power flow imbalance or changes in the characteristics of the HV transmission line 108. A local clock coupled to the master control module is configured to command a start of impedance injection and a stop of the impedance injection by the identified IIUs 600 as resource. The impedance injection is controlled by master control module 503, wherein the local clock is synchronizable with other local clocks in the one or more distributed IIMs and also clocks in the LINCs coupled to the IIMs 300.

According to one embodiment, a method for synchronized injection of impedance on to a high voltage (HV) transmission line 108 is disclosed. The method is performed by an impedance injection module (IIM) 300 coupled to the HV transmission line 108. One disclosed method includes identifying disturbance, power flow imbalance or changes in characteristics of the HV transmission line by the master control 503 of the IIM 300. The method may also include receiving a command from the network operator/supervisory utility 206 and providing an interactive response to the command from the network operator/supervisory utility 206 who identifies problems or system control needs of the grid system and provide commands and interactive control instructions. The method may further include defining, by an intelligent master control module 503, an impedance injection waveform in response to the identified disturbance or imbalance, generating injection information comprising synchronization timing based on the generated impedance injection waveform, sending the injection information to one or more neighboring IIMs 300, identified as available resources, and initiating impedance injection on to the HV transmission line based on the injection information.

According to an embodiment, a system for injecting impedance on to an HV transmission line using multiple distributed IIM 300 comprising multiple TL-FACTS-based IIUs 600 is disclosed. As an example: The system includes one or more TL-FACTS-based IIUs 600 connected in a series and/or parallel combination to be a first IIM 300 having a first coordinated impedance injection capability on to the HV transmission line 108, and where applicable, a second group of TL-FACTS-based IIUs 600 connected in series and/or parallel combination to be a second IIM 300 having a second coordinated impedance injection capability on to the HV transmission line 108. The first group of TL-FACTS-based IIUs 600 and the second group of TL-FACTS-based IIUs 600 form two IIMs 300 that are distributed and connected in series with the HV transmission line 108, and are enabled for high-speed sub-cyclic communication. Each IIU 600 of each group is enabled to inject rectangular impedance, typically in the form of a voltage, on the HV transmission line based on the generated injection information for impedance injection comprising synchronization timing established by a master control 503 of the IIM 300 that recognized a disturbance. In order to reduce harmonic oscillation on the HV transmission line 108, the master control 503 is enabled to generate the impedance injection information such that the impedance injection from each IIU 600 be timed in such a manner that when aggregated the injected impedances form a pseudo-sinusoidal waveform. By synchronizing the time delay between the impedance injection from each of the IIUs 600 in a coordinated fashion, the first and the second impedance injections are enabled to cumulatively form the pseudo-sinusoidal impedance waveform for injection on to the HV transmission line.

In the case where the available resources in one local area are insufficient and additional resources are needed to respond to a disturbance, the controller 503 of the IIM 300 identifying the resources is enabled to connect to and access the needed additional resources from neighboring local areas via the high-speed communication capability to the LINCs 302 and through it to the neighboring LINCs 302.

There are four possible ways to implement the time synchronization of the clocks associated with the IIMs 300 (as previously discussed).

1. Using a master controller with a master clock that provides commands to the master control of each IIM 300 to start and stop impedance injection from the TL-FACTS-based IIUs 600 constituting the IIM 300 at the appropriate time. Typically, in this implementation the master controllers 503 is in the LINCs 302 which are enabled with high-speed communication links to the distributed IIMs 300 and to neighboring LINCs 302. In a LINCs 302 alone based implementation, the master controller 503 in the LINCs 302 are the only units that have clocks and instructions are transmitted over high-speed communication links to the distributed IIMs 300. Such a system will fail any time the communication link fails. Hence this type of implementation though lower in cost is not optimal.

2. Using the frequency and phase of the current flowing on the power line to establish a relative time, where one such method being by zero crossing detection to establish relative time. Each local master control module 503 has within it a zero-crossing detection capability and all commands as to when to start injection and when to stop injection are provided to the TIM 300 relative to the zero crossing. The IIMs rely on zero crossing as a reference for their internal timers. These have the disadvantage that correction of transmission frequency by impedance injection works better when used with an absolute time. Also, disturbances on the line can cause the timers to miss zero crossing events. This is a low-cost method but is not a reliable method at present, and hence not the preferred implementation.

In both the above cases the local master controllers do not have clocks associated with them. Hence they are lower cost solutions that depend on external clocks or zero crossing waveforms to initiate action. In general, these are not optimum for providing high speed corrective action to problems on the HV transmission lines.

3. Using local master controllers with synchronizable clock that is synchronized to a master clock at the utility 206 or LINCs 302 is the third option. In this case, a master controller either in the utility 206 or LINCs 302 can provide instructions and commands to the distributed IIMs 300 which can be temporarily stored. The TL-FACTS-based IIUs 600 included in the IIMs 300 then inject impedances on to the HV transmission line according to the received and stored instructions. Intermittent communication failures do not impact the operation of the IIMs 300 in this instance as the local clocks can still function in a synchronous mode if the link gets re-established in short order. Hence for implementation on the grid system this is the currently preferred implementation.

FIG. 6A is a circuit block diagram illustrating a local master control module of a TL-FACTS-based IIU having an associated local clock according to one embodiment. In FIG. 6A, local master control module 503 of an IIM (e.g., IIM 300) that is coupled to a local clock 606A that can be synchronized to a clock associated with the utility that connects with the LINC 302 and, using the communication capability connects to the local clocks of the IIM to provide local synchronization among all the local IIMs 300. Such a clocking system is simple to implement and provides the capability to synchronize all the local clocks of IIMs 300 connected under a LINC 302 by using the high-speed communication links 303 connecting all LINCs 302 across all IIMs 300 over the grid system 200A. Instructions downloaded to the local master control module 503 can be executed by the IIM 300 in a time synchronized fashion even if the communication links fail, as the local clocks retain synchronization for some period of time. The main disadvantage of such a system is that in the case of a long-time failure of the communication link 305 from the utility to the LINCs 302 or a failure of the high-speed link 303 from the LINCs 302 to the IIMs 300, the local clocks 606A associated with the local IIMs 300 can go out of synchronization.

4. A fourth option is to have the local master controller with clocks that sync with a global master clock such as Global Positioning System (GPS) clock. This is the most accurate option and is shown in FIG. 6B.

FIG. 6B is a circuit diagram illustrating a local master control module of a TL-FACTS-based IIM having an associated local clock that can be synchronized to a global clock according to one embodiment. In FIG. 6B, local master control module 503 having a local clock 606B associated therewith that can be synchronized to a global master clock such as GPS clock 607 to provide synchronization across the local and global IIMs 300 on the grid system 200A. Such a system is more complex and more expensive but ensures that in the case of any communication failure, the local clock 606B continues to function in a synchronized fashion providing any necessary synchronization input to the master control module 503 of the IIMs 300 and keeping the local and global IIMs 300 on the grid system 200A synchronized.

The embodiments are shown as examples only and other synchronization methods are also possible, such as having a GPS synchronizable clock on the LINCs 302 which is used to synchronize the local master clock modules associated with the IIMs 300 via the high-speed communication link 303. In such a case a failure of the communication between the LINCs 302 and the local controller 606A will result in the local IIMs 300 connected to the specific LINC 302 going out of sync while others across the grid 200 continuing to function correctly.

FIG. 7 is a block diagram illustrating an IIM having a series-parallel connection of TL-FACTS-based IIMs according to one embodiment. In FIG. 7, four TL-FACTS-based IIUs 600-1 to 600-4 collectively form (or included as part of) impedance injection module 300, which is to be suspended from a power line (e.g., HV transmission line 108). In one embodiment, IIUs 600-1 and 600-2 are connected in parallel, and IIUs 600-3 and 600-4 are also connected in parallel. In one embodiment, the two sets or pairs of parallel connected IIUs 600-1, 600-2 and 600-3, 600-4 are connected in series to form IIM 300. When a sinusoidal wave travels down the high voltage (HV) the power line 108, the time delay is t1 between the two pairs of IIMs.

The IIM 300 may include a single or a plurality of IIUs 600 (e.g., four or more as described above) interconnected in series-parallel configuration that can also be used as a basic subsystem unit in mobile power flow control application or installed at substations in some embodiments. FIG. 7A shows another exemplary and non-limiting implementation of IIM 300 as a power flow control subsystem 700A with multiple IIUs 600 in a series-parallel connection with ‘m’=3 IIU 600 connected in a series string as shown in 702A with ‘n’=3 such strings connected in parallel as shown in 703A to form the IIM 300 as subsystem 700A in an exemplary mobile power flow control application. A bypass protection switch 701A is shown which is used to protect the interconnected IIUs of the subsystem 700A in case of power surges and power system breakdown.

FIG. 7B shows an exemplary implementation of a mobile platform with three subsystems 700A on a mobile carrier 704B (e.g., a vehicle such as a trailer or any other wheeled vehicle capable of carrying equipment), with the subsystems 700A on insulators 702B that insulate them from ground and the sub-systems spaced way by a distance ‘S’ from each other in one embodiment. In one embodiment, the mobile carrier 704B is transportable to any remote or substation locations to provide power grid monitoring and control capability as required by the supervisory utility 206 for control and management of the total power system 200 for example.

FIG. 7C shows the mobile platform 700B with three connections to the three phases of high-voltage powerlines 108 of power grid 700C. The three subsystems 700A are connected in series with the HV power lines 108 by breaking the HV power line 108 and supporting the two ends by insulator 701C to retain the tension of the HV power line. In one embodiment, each subsystem 700A (which may be a transformer-less subsystem) is then connected across the cut ends using connectors 702C.

FIG. 8 is an exemplary block diagram illustrating the time delay between an exemplary group of IIMs distributed on an HV transmission line. Referring to FIG. 8, a set of four IIMs 300, each having four TL-FACTS-based IIUs connected in series-parallel combination (as previously described). The four IIMs 300 are designated as 300 a, 300 b, 300 c and 300 d distributed over the HV transmission line 108. The power line 108 is typically suspended from towers 201 and isolated from the towers, though they can also be connected to the power lines in other ways, such as installed on mobile platforms and connected to the power line therefrom or in a substation area to provide redundancy and expansion capability. The time delay between the IIMs 300 a and 300 b is designated as t2, the time delay between 300 b and 300 c is designated as t3, and the time delay between 300 c and 300 d is also designated as t2, as shown in FIG. 8.

FIG. 9 is a diagram illustrating an exemplary smoothed sinusoidal waveform formed from a plurality of rectangular injected waveforms that are timed and synchronized. In FIG. 9, an example of a buildup of a pseudo-sinusoidal impedance waveform from 16 injected rectangular waves 902 is shown. The sinusoidal wave 901 is formed by smoothing out the cumulative impedance injections. The impedance injections are rectangular in shape. In one embodiment, a single impedance injection unit with a group of 16 TL-FACTS-based IIUs (e.g., IIU 600) in parallel connection attached to the HV transmission line can inject the exemplary 16 rectangular waveforms 902 from a single location with easy synchronization of the waveforms as shown. But this type of installation results in a large and heavy IIM 300, which makes it difficult to be supported directly on the HV transmission line. It also increases the cost of such IIMs as they are dedicated for high value impedance injection. When the IIMs 300 are lower weight series-parallel configurations, as shown previously, distributed over the HV transmission line 108, the synchronization and control for formation of the injected waveforms 902 become more difficult without the high-speed intercommunication and local synchronization of the clocks between the local IIMs 300 distributed across the HV transmission line and also the high-speed intercommunication between the neighboring LINCs 302.

FIG. 10 is a diagram illustrating exemplary time-synchronized injection of rectangular waveforms injected on to an HV transmission line to achieve a pseudo-sinusoidal waveform. In FIG. 10, the injected waves from the groups of TL-FACTS-based IIUs 600-1 to 600-4 of FIG. 7 forms an IIM 300. Four such IIMs 300 a-d, distributed over the HV transmission line 108 are shown in FIG. 8 as being used as resources for generation of the aggregated injected impedance waveform. The injected impedance from each of the TL-FACTS IIUs is identified by its designation 600-xy (e.g., 600-1 a, 600-2 a, 600-3 a, and so on) where x is the designator number of the TL-FACTS-based IIU 600 in the IIM 300 and y is the designation of the IIM 300 a, b, c or d, respectively. In this example, the amplitude of the injected waveform from each TL-FACTS-based IIU 600 is assumed to be a constant value 1002, though this is not mandatory. As shown in FIG. 10, the amplitudes of injected impedances are constant, though this is not mandatory as long as the variations are taken into account in the time delays for generating the pseudo sinusoidal waveform. The impedance injection waveform of each of the 16 TL-FACTS-based IIUs 600 from the four IIMs 300 distributed over the HV transmission line in this case has to be synchronized for start of injection and stop of injection, with the impedance injections from the other 15 TL-FACTS IIUs to generate the pseudo-sinusoidal waveform. The start times 1101 and stop times 1102 requirement for generation and injection of the impedance injection are shown in FIG. 11. The duration of injection is shown in FIG. 10. In the case of mobile container based application, such as in a mobile system control application including power flow control or in a fixed location system control application including power flow control, such as a substation application, the time delays are negligible and only the synchronized and timed injection delays have to be taken care of in generating the necessary waveforms.

Since the IIMs 300, a, b, c, and d are distributed over the HV transmission line, the delays indicated in FIGS. 8 and 9 have to be accounted for to get the pseudo-sinusoidal waveform. The delays for the synchronization of the waveforms from the four IIMs 300 are shown in Table 1 of FIG. 14, including the start delay. For ease of understanding the first start is designated t0 and all others are shown referencing the t0 time.

Since the speed of transmission over the HV transmission line 108 is very fast, a 300-meter separation between IIMs will incur only a delay of about 1 to 2 microseconds. The transmission delays can be typically ignored at the present time and impedance injection can be synched to a time across a plurality of IIMs 300 a-d. The method as described provides additional accuracy to the impedance injection scheme for future applications.

Having built-in intelligence and synchronizable clocks with high-speed communication capability 410 in each of the locally interconnected group of IIMs 300 a-d with a local supervisory LINC 302 enable the set of IIMs to be locally and globally time synchronized. This helps to consistently generate the needed delays across the locally connected IIMs 300 to work as a group, to generate and inject the pseudo-sinusoidal waveform on to the HV transmission line.

It should also be noted that the examples described are for clarifying the invention and not meant to be limiting. For example, many more than four TL-FACTS-based IIUs 600 may be used to form IIM 300 and a plurality of IIMs 300 distributed over the HV transmission line 108 communicatively interconnected in a local area connection can be used to generate and inject the needed impedance value with the needed number of synchronized injection waveforms to generate a pseudo-sinusoidal impedance waveform. It should also be noted that a similar waveform can be generated and injected in the other (negative) half cycle time as well.

Other exemplary embodiments may have indicated the mobile platform and substation implementations where no time delays exist as all IIUs 600 are co-located.

In addition to the examples of implementation above, having time synchronized intelligent IIMs 300 with sufficient processing power enables the IIMs 300 to provide interactive control for utilities for system management and also enables the IIMs 300 to recognize any disturbances and power flow imbalances locally on the high voltage power lines, coordinate with other distributed IIMs 300s, and generate the appropriate waveforms necessary to overcome such disturbances and power flow imbalances. The intelligent IIMs 300s are also able to identify the available resources (e.g., available IIMs) in the local and global grid 200, for example, using the communication system to enable an integrated waveform generation capability using these resources when additional resources are needed to take corrective action. Such a local self-aware intelligent system control block diagram is shown in FIG. 12. The local master control 503 in this exemplary system includes an intelligent processing engine 1201 that provides the intelligence and independent decision-making capability to the IIM 300. The sensors attached to the power lines sense and extract the condition of the HV transmission line to which they are coupled. The sensors provide the sensed information typically to the utility in one embodiment and in another embodiment described here the information is sensed locally and provided to a local module that is a disturbance/flow imbalance identifying module 1202 that identifies changes in the characteristics of the HV transmission line.

In all the cases, whether it is the embodiment where the utility receives the sensed information and provide the commands in response to the received information, or the embodiment where the sensing and flow control is locally handled, the utility is enabled to provide interactive instructions and commands to the local IIMs for impedance injection to meet target grid system control objectives. In this case the local disturbance/flow imbalance identification module 1202 is unused as the IIMs 300 respond interactively to the commands and instructions for impedance injection from the supervisory utility 206. These impedance injection instructions received by the IIM 300 in this embodiment are passed to the local injection definition module 1203 for execution.

In the embodiment shown in FIG. 12 and described herein, the identified changes of the HV power line are passed to the injection definition module 1203 for corrective execution by the disturbance/flow imbalance identification module 1202.

A local injection definition module 1203 uses the instructions received from the supervisory utility 206 in the first embodiment or the identified disturbance data from 1202 in the second embodiment to define the response waveform to be injected. A resource check and resource identification module 1204, in high-speed communication with the local IIMs 300s and the LINC 302 via communication links 303, through a communication module 1206, collects the information on the availability of resources to achieve the necessary injected impedance waveform. An injection detail decision module 1205 generates the detailed injection needs by each of the identified resource available to the IIMs 300. A start of injection time, an end of injection time, and amplitude of injection for each of the identified resources comprise the details. This information is transmitted to the respective resource IIM 300 over the high-speed communication link 303 by the communication module 1206 over wireless connection established using the wireless communication capability 410. Once the response capabilities for corrective action to be taken for the disturbance on the HV transmission line are established and communicated, an injection initiation and monitoring module 1207 initiates the injection of the waveform and monitors its progress, via the high-speed communication links of the communication module 1206. The monitoring module 1207 will continue to monitor and repeat the injection until the imbalance is corrected or the root cause of the disturbance is removed.

FIG. 13 is an exemplary flow diagram of the process for providing HV transmission line control using synchronized injection of impedance according to one embodiment. The process, for example, may be performed by an intelligent IIM (e.g., IIMs 300 a-d), and the distributed IIMs 300 having their clocks synchronized across the grid or responding interactively to commands and information from supervisory utility (as defined by S1302).

At step S1301, sensors coupled to the HV power transmission line sense changes in the grid characteristics (e.g., temperature increases or vibration) and power flow.

Two options exist for handling the sensed data as shown at step S1302.

In a first embodiment (option 1), the sensed information is transmitted to the supervisory utility 206 at step S1303A. The supervisory utility processes the received data and generates and provides control commands for impedance injection back to a local master controller in an IIM as shown at step S1304A.

In a second embodiment (option 2), the sensed data is sent to the local master control 503 of the IIM 300 as at S1303B. A disturbance identification module 1202 of the local master control 503 identifies the type of local problems and disturbances on the grid from the extracted information and generates instructions for impedance injection (S1304B).

The local master controller 503 with the intelligence and processing capability 1201 built into the IIM 300 receives the impedance injection instruction and creates an impedance injection solution, in the form of a waveform that can resolve the identified problem or disturbance and re-establishes stability to the HV transmission line 108 of the grid 200 (S1305).

The IIM 300 then with the communication capability 1206 having hi-speed links 303 connecting it to the local distributed local IIMs 300s, identify the active resources that may or may not be FACTS devices and controllers that are readily available to generate the necessary waveform of the impedance injection solution using resource check and identification module 1204 of the local master controller 503 (S1306).

If the local area resources available to the IIM 300 are insufficient for generation of the waveform of the impedance injection solution, the resource availability of the neighboring location IIMs 300 connected through the LINCs (e.g., LINCs 302), or even the further out, distributed IIMs 300 available on the high voltage transmission line are identified for use in generation of the impedance injection waveform to resolve the problem or disturbance on the HV transmission line of the grid (S1307).

For example, IIM 300A, using the intelligence and processing power built in, further extracts the capability of each of the identified resources and puts together an impedance generation and injection pattern which has the time of the start of injection, the amplitude of the injection and the stop time of the injection to generate the necessary sequence, that, when combined, produce the waveform shape and amplitude to overcome the problem or disturbance on the grid 200 (S1308).

The impedance injection pattern for generation of the response impedance waveform for injection on to the HV transmission line 108 is provided to the respective identified resource via the high-speed communication links 303 (S1309).

The identified distributed IIMs 300 identified as available resources, interactively working together in time synchronization, are able to produce the necessary impedance injection waveform and inject it on to the high voltage power lines of the grid (S1310).

The combined injected pseudo-sinusoidal waveform, generated by the aggregation of the individual injected impedance waveforms, is smoothed by the impedance of the HV transmission line to reduce any unwanted oscillations due to the impedance injection while providing the required impedance injection response for system control. (S1311).

Even though the invention disclosed is described using specific implementations as examples, it is intended only to be exemplary and non-limiting. The practitioners of the art will be able to understand and modify the same based on new innovations and concepts, as they are made and become available. The invention is intended to encompass these modifications that conform to the inventive ideas discussed. 

What is claimed is:
 1. A system for injecting impedance on to a high voltage (HV) transmission line, the system comprising: a plurality of sensors distributed over and coupled to the HV power line configured to detect changes in power flow over the HV power line and changes in characteristics of the HV power line and transfer the sensed data to a local impedance injection module (IIM); one or more distributed impedance injection modules (IIMs), each distributed IIM comprising one or more transformer-less flexible alternating current (AC) transmission system (TL-FACTS) based impedance injection units (IIU)s coupled to the HV transmission line, each TL-FACTS-based IIU including: a master control module configured to receive sensed data from one or more local sensors and generate instructions for impedance injection as a response to the detected changes, identify the IIMs available for impedance injection as resources for impedance injection on the HV transmission line, and generate and provide switching control signals to the identified resources for controlling impedance injection from the identified resources in response to the detected changes in HV power line characteristics and changes in power flow on the HV transmission line; and a local clock coupled to the master control module and configured to command a start of impedance injection and a stop of the impedance injection controlled by master control module, wherein the local clock is synchronizable with other local clocks in the distributed IIMs.
 2. The system of claim 1, wherein the local clock in each TL-FACTS-based IIU is synchronized with a phase and frequency of current to establish a relative time to command the start and stop of the impedance injection.
 3. The system of claim 1, wherein the local clock in each TL-FACTS-based IIU is synchronized with a master clock at one of a local intelligence center or a supervisory utility overseeing the system.
 4. The system of claim 1, wherein the local clock in each TL-FACTS-based IIU is synchronized with a master global clock to command the start and stop of the impedance injection.
 5. The system of claim 1, wherein each TL-FACTS-based IIU further includes a high-speed communication interface for sub-cyclic communication with another IIM within a local area and local intelligence centers for transfer of the switching control signals from the master control and for coordinating impedance injection of the identified resources and also to respond to any locally detected disturbances or imbalances on the HV transmission line for control of line current and line balancing within the local area, and each distributed IIM is enabled to respond interactively to instructions from the supervisory utility to meet target grid system objectives.
 6. The system of claim 1, wherein each TL-FACTS-based IIU further includes a plurality of flexible alternating current transmission systems (FACTS) switches collectively forming the TL-FACTS-based IIU.
 7. A system for injecting impedance waveform on to a high voltage (HV) transmission line, the system comprising: a plurality of sensors distributed over and coupled to the HV power line, the sensors configured to sense and monitor the HV power line for changes in power flow and changes in characteristics of the HV power line, and to transfer sensed and monitored data from the sensors to a supervisory utility for analysis and generation of instructions to command one or more distributed impedance injection modules (IIMs) on the HV transmission line to meet a target grid system objective, each IIM comprising one or more transformer-less flexible alternating current (AC) transmission system (TL-FACTS) based impedance injection units (IIU)s coupled to the HV transmission line, each IIM including: a master control module configured to receive instructions from the supervisory utility and identify an impedance injection waveform as a response to meet the target grid system objective; identify the IIMs available for impedance injection as resources on the HV transmission line, and generate and provide switching control signals to the identified resources for controlling impedance injection from the IIUs of each of the identified resources to generate the identified impedance injection waveform; and a local clock coupled to the master control module and configured to command a start of impedance injection and a stop of the impedance injection controlled by master control module, wherein the local clock is synchronizable with other local clocks in the distributed IIMs; wherein synchronized injections of the impedance waveforms from the identified resources are aggregated to generate the impedance injection waveform as the response to meet the target grid system objective.
 8. The system of claim 7, wherein each TL-FACTS-based IIU further includes a high-speed communication interface for sub-cyclic communication with another IIM within a local area and local intelligence centers for transfer of the switching control signals from the master control and for coordinating impedance injection of the identified resources to respond to instructions from the supervisory utility to meet target grid system objectives.
 9. The system of claim 7, wherein the local clock in each IIM is synchronized to one of a master-clock at the utility supervisory or a master-global-clock.
 10. The system of claim 1, wherein the TL-FACTS-based IIUs respectively inject impedance on to the HV transmission line at different start and stop times such that an aggregation of rectangular waveforms produced by the TL-FACTS-based IIUs of the IIMs identified as the resources generate a pseudo-sinusoidal impedance waveform when injected on the HV transmission line.
 11. A method for synchronized injection of impedance on to a high voltage (HV) transmission line, the method being performed by a plurality of impedance injection modules (IIMs) coupled to the HV transmission line, the method comprising: identifying disturbance or power flow imbalance on the HV transmission line or receiving a command from supervisory utility for meeting a target grid system objective; defining an impedance injection waveform in response to the identified disturbance, power flow imbalance or the command received from the supervisory utility; generating injection information based on the defined impedance injection waveform; sending the injection information to one or more local IIMs; and initiating impedance injection on to the HV transmission line based on the injection information.
 12. The method of claim 11, further comprising: determining whether local resource from the one or more local IIMs is available to generate the impedance injection waveform; and in response to determining that the local resource is available, generating the impedance injection waveform using the local resource.
 13. The method of claim 12, further comprising: in response to determining that the local resource from the one or more local IIMs is unavailable, identifying one or more IIMs in a neighboring location having available resource to generate the impedance injection waveform; and generating the impedance injection waveform using the available resource of the one or IIMs in the neighboring location.
 14. The method of claim 11, wherein the injection information includes a start time of injection, a stop time of injection, and an amplitude of the impedance injection waveform.
 15. The method of claim 14, wherein the start time and the stop time are synchronized with a phase and frequency of current in the HV transmission line as a relative time.
 16. The method of claim 14, wherein the start time and the stop time are synchronized with a master clock at a supervisory utility.
 17. The method of claim 14, wherein the start time and the stop time are synchronized with a master global clock.
 18. The method of claim 11, wherein the injection information is sent to the one or more local IIMs through a local intelligence center (LINC) that is communicatively coupled to the one or more local IIMs for high-speed communication.
 19. The method of claim 11, wherein the local IIMs utilize the injection information to respectively injective impedance on to the HV transmission line at different start and stop times of injection to enable a buildup of a pseudo-sinusoidal impedance waveform.
 20. A system for injecting impedance on to a high voltage (HV) transmission line, comprising: groups of transformer-less flexible alternating current (AC) transmission systems (TL-FACTS) based impedance injection units (IIUs) connected in a series-parallel configuration that are used as impedance injection modules (IIMs) distributed over a high-voltage (HV) transmission line; wherein a first IIM having a first group of TL-FACTS-based IIUs is coupled to the HV transmission line and provides a first group of impedance injections on to the HV transmission line; and a second IIM having a second group of TL-FACTS-based IIUs is coupled to the HV transmission line and provides a second group of impedance injections on to the HV transmission line; wherein the first IIM and the second IIM are connected in series over the HV transmission line for providing the first and second groups of impedance injections; wherein time delays between respective impedance injections from the TL-FACTS-based IIUs are all synchronized to form a pseudo-sinusoidal impedance waveform when injected impedances are aggregated on the HV transmission line.
 21. The system of claim 20, wherein the distributed IIMs are assembled on a mobile platform that is transportable and deployable along the HV transmission line including at sub-stations, and connected to the HV transmission line for impedance injection.
 22. The system of claim 20, wherein each TL-FACTS-based IIU from the first and second groups of TL-FACTS-based IIUs comprises: a sensor configured to detect disturbance or imbalance on the HV transmission line; a master control module configured to provide switching control signals for controlling impedance injection in response to command inputs from a supervisory utility or the detected disturbance or imbalance on the HV transmission line for control of line current and line balancing and grid control targets; a local clock coupled to the master control module and configured to command a start of impedance injection and a stop of the impedance injection controlled by master control module, wherein the local clock is synchronizable with other local clocks in the first and second groups of TL-FACTS-based IIUs to coordinate the impedance injection on to the HV transmission line based on the switching control signals.
 23. The system of claim 22, wherein each TL-FACTS-based IIU further comprises a high-speed communication interface for sub-cyclic communication with other TL-FACTS-based IIUs within a local area in response to the detected disturbances or imbalances on the HV transmission line for control of line current and line balancing within the local area.
 24. The system of claim 22, wherein the local clock of each TL-FACTS-based IIU is synchronized with (i) a line current and frequency-based detection signal as a relative time, (ii) a master clock at a supervisory utility overseeing the system, or (iii) a master global clock.
 25. The system of claim 22, wherein the first and second groups of TL-FACTS-based IIUs respectively inject impedances on to the HV transmission line at different start and stop times such that the rectangular waveforms produced from the first and second groups of TL-FACTS-based IIUs, when aggregated, generate the pseudo-sinusoidal impedance waveform. 